BoilerFaultCodesThe 4 most common faults
01
Lock-out High DIY-safe
Your boiler has stopped working as a safety precaution because it failed to ignite, so it is currently waiting for a manual reset.
What to try first
Ensure your oil tank has sufficient fuel and the supply valve is openLocate the red reset button on the burner casing and press it firmly onceWait for the boiler to attempt an ignition sequence; if it locks out again, do not force it
02
Overheat High Engineer
Your boiler has detected that it is getting dangerously hot and has shut itself down to prevent any internal damage.
Full guide for Overheat03
10 Emergency Engineer
Your boiler is struggling to push smoke and exhaust gases out properly during startup, which can lead to fumes leaking into your home.
Full guide for 1004
12 Emergency Engineer
Your boiler is detecting that exhaust fumes are leaking inside or near the unit instead of going properly up the chimney flue.
Full guide for 12on the Grant Vortex Pro
PhotocellIgnition electrodesOil nozzleControl boxHigh limit thermostatCirculating pump
Based on parts cited in our fault code database. Your engineer will confirm what's actually needed after diagnosis.
Call a Gas Safe engineer if…
- You can smell gas or see signs of a leak
- The Grant shows an Emergency or High severity code
- The boiler keeps locking out after repeated resets
- You've tried the DIY checks and the fault hasn't cleared
- There's visible water leaking from the boiler
- The flame is yellow or orange instead of blue
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